1. Field of Invention
The present invention relates generally to an apparatus for processing semiconductor wafers. More specifically, the invention relates to a lift-pin assembly for moving semiconductor wafer using in a semiconductor wafer-processing chamber.
2. Description of the Background Art
Integrated circuits have evolved into complex devices that include millions of transistors, capacitors and resistors on a single chip. The evolution of chip design results in faster circuitry and greater circuit density. As the demand for integrated circuits continues to rise, chip manufactures have demanded semiconductor process tooling having increased wafer throughput and greater product yield. To meet this increase in throughput, tooling is being developed to process wider diameter wafers, for example, wafers having diameters of 300 millimeters (mm).
Processing chambers generally capable of processing 300 mm substrates transport and support the substrate by a lift-pin assembly. Such lift-pin assembly can be used for temporarily supporting the substrates during transfer, thermal, chemical, optical and other treatments of the substrate. In order to transfer a substrate such as a wafer into a substrate processing chamber, it is conventional to utilize a robot arm and lift-pin assembly such as the types disclosed in U.S. Pat. Nos. 4,431,473, and 5,215,619. Specifically, a wafer is supported by three pins dispersed approximately 120 degrees apart and projecting from a lifter ring. The lifter ring is attached to a robotic arm. The lift-pins are supported on the lifter ring forming part of a substrate support assembly wherein the lifter ring is movable in a vertical direction between upper and lower positions. The lifter ring is movable such that the lift-pins have an upper surface located above the substrate support surface of the substrate holder when the lifter is in the upper position. Furthermore, the upper surface of the lift-pin is below the substrate support surface when the lifter ring is in the lower position. Thus, part of each lift-pin passes through a respective lift-pin hole in the substrate support when the lifter ring moves from either the lower position to the upper position. To drive the lifter ring, an actuator, such as a conventional pneumatic cylinder is generally used. The cylinder drives the lifter ring in the up or down positions, which in turn drive the lift-pins that raise or lower the wafer.
One problem that has been observed is that the lift-pins may bind as they pass through the lift-pin holes in the substrate support. Another problem is that the increased size in the industry from 200 mm to 300 mm wafers requires redesign of the processing chambers and accordingly, the lift-pin assemblies with regard to their configuration with other components in the substrate support assembly.
Therefore, there is a need in the art for a lift-pin assembly that does not bind in the lift-pin holes of the substrate support as the pins are raised or lowered. Moreover, it would be desirable for such a processing system to minimize the number of components and provide ease of serviceability.